This invention relates to a method and apparatus for reduced pressure induction heated deposition. More specifically, the invention relates to the low pressure, induction heat epitaxial deposition of thin layers on semiconductor bodies.
The processing of many of the various semiconductor devices and circuits requires the growth of an epitaxial layer of semiconductor material onto a polished semiconductor substrate. At present, the growth of that epitaxial layer is one of the most expensive operations in the processing sequence. Almost all epitaxial layers are grown at atmospheric pressure in an RF induction heated reactor. This method for epitaxial growth, although widely used, has a number of serious drawbacks. Chief among these drawbacks are inefficient use of both reactant gases and power, non-uniformity of thickness and resistivity of the resulting epitaxial layer, auto-doping from the substrate, and, most importantly, low throughput. A number of attempts have been made to overcome one or more of these difficulties. It is recognized, for example, that most of the above-mentioned shortcomings could be overcome by carrying out the deposition at a reduced pressure. U.S. Pat. Nos. 3,900,597 and 4,098,923, for example, demonstrate the advantages of the low pressure deposition of polycrystalline silicon and pyrolytic silicon dioxide, respectively. The disclosures of these two patents, however, are not directly applicable to the growth of epitaxial layers for several reasons. Those disclosures show the deposition taking place in a hot-walled reaction tube continuously heated in a conventional resistance heated furnace. At the higher temperatures encountered in epitaxial growth (greater than about 900.degree. C. for epitaxial silicon growth), deposition on the hot reactor tube wall causes the wall to weaken and finally to implode. Additionally, a clean, oxide-free substrate surface is essential for high quality epitaxial growth; but loading wafers into a continuously hot furnace without surface oxide formation is very difficult. Further, it is difficult to carry out the usual pre-growth, in situ etch of the surface with hydrochloric acid without also encountering a pre-reaction of the hydrochloric acid with material previously deposited on the reactor tube walls. And finally, deposition on the reactor walls tends to inhibit the desired epitaxial growth and makes it extremely difficult to achieve growth rates in excess of about 0.02 micrometers per minute.
One attempted solution is embodied in a radiant heated reduced pressure epitaxial reactor. Such reactors are operated, however, only at pressures of greater than about 80 torr (10.7 kPa). At this pressure there is some reduction in autodoping, but the full advantages of low pressure deposition, especially improved throughput, cannot be achieved at these pressures.
A further attempted solution is to use a cold wall, RF induction heated reactor, but such a reactor has not heretofore been feasible. At pressures less than about 150 torr (20 kPa), arcing tends to occur within the reactor. The arcing tends to occur between the susceptor and the end caps, and from the high potential to low potential ends of the suspector. The arcing or glow discharge inhibits normal epitaxial growth and results in extremely poor quality films.
Accordingly, a need existed to develop an apparatus and method for the reduced pressure, induction heated deposition of thin layers onto a substrate which would overcome the problems inherent in the prior art apparatus and methods.
It is therefore an object of this invention to provide a method and apparatus for the high volume deposition of uniform, high quality layers.
It is a further object of this invention to provide an apparatus for the reduced pressure, induction heated deposition of thin layers onto an object within the apparatus.
It is another object of this invention to provide an apparatus for low pressure deposition in which glow discharge arcing is suppressed.
It is still further object of this invention to provide a high volume process for the deposition of uniform epitaxial layers on semiconductor substrates.